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Efficient Variable Automatic Buffers

Efficient Variable Automatic Buffers

Listing 3: Extract from stlsoft_auto_buffer.h.

/* /////////////////////////////////////////////////////////////
 * Extract from stlsoft_auto_buffer.h
 * www:    http://www.stlsoft.org/
 * Copyright (C) 2002-2003, Synesis Software Pty Ltd.
 * (Licensed under the Synesis Software Standard Source License:
 *  http://www.synesis.com.au/licenses/ssssl.html)
 * ////////////////////////////////////////////////////////// */
// class auto_buffer
template< typename  T
        , typename  A
        , size_t    SPACE = 512
class auto_buffer
  : protected A
  typedef T                         value_type;
  typedef A                         allocator_type;
  typedef size_t                    size_type;
  typedef auto_buffer<T, A, SPACE>  class_type;
  typedef value_type                *pointer;
  typedef value_type const          *const_pointer;
  typedef value_type                *iterator;
  typedef value_type const          *const_iterator;

// Implementation
  static allocator_type &_get_ator()
    static allocator_type   s_allocator;

    return s_allocator;
  allocator_type &_get_ator()
    return *this;

// Construction
  explicit auto_buffer(size_type cItems)
    : m_buffer( (space < cItems) 
                  ? _get_ator().allocate(cItems, 0)
                  : m_internal)
    , m_cItems( (m_buffer != 0)
                  ? cItems
                  : 0)
    // These assertions ensure that the member ordering is not
    // changed, invalidating the initialisation logic of 
    // m_buffer and m_cItems. The runtime assert is included
    // for compilers that don't implement compile-time asserts.
      stlsoft_raw_offsetof(class_type, m_buffer) < 
      stlsoft_raw_offsetof(class_type, m_cItems));
      "m_buffer must be before m_cItems in the auto_buffer definition",
      stlsoft_raw_offsetof(class_type, m_buffer) < 
      stlsoft_raw_offsetof(class_type, m_cItems));

    // Use the type_is_non_class_or_trivial_class constraint to ensure that 
    // no type is managed in auto_buffer which would result in dangerous 
    // mismanagement of instances lifetimes.
    // Preprocessor specification of _STLSOFT_AUTO_BUFFER_ALLOW_NON_POD
    // prevents this, but the natural rules of the language will
    // still prevent non POD types being placed in m_internal[].
    if(space < m_cItems)
      stlsoft_assert(m_buffer != 0);

      _get_ator().deallocate(m_buffer, m_cItems);
// Operators
  operator pointer ()
    return m_buffer;
  operator const_pointer () const;
// Iteration
  const_iterator begin() const
    return m_buffer;
  const_iterator end() const
    return m_buffer + m_cItems;
  iterator begin();
  iterator end();
// Attributes
  size_type size() const
    return m_cItems;
// Members
  enum  { space = SPACE  };

  value_type *const m_buffer;           // Pointer to used buffer
  size_type const   m_cItems;           // Number of items in buffer
  value_type        m_internal[space];  // Internal storage
// Not to be implemented
  auto_buffer(class_type const &rhs);
  auto_buffer const &operator =(class_type const &rhs);
/* ///////////////////////////////////////////////////////////// */

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